I got a Kodak Ektar 203mm f/7.7 lens mounted on a Sychro-Compur #1 labeled Graphic. I like it because it has more character than modern lenses and is easier to handle than vintage lenses, but I don't know what size filter will fit this lens. The same lens I see often on Ebay today will fit Kodak series filters, but this seems to have a different thread. The unique number on the lens is marked OY, so this was probably the last production lens shipped in 1960. I initially assumed this was a 37mm, but it could not be mounted, then I tried a Kenko 36.5mm, which also could not be mounted. I have asked people who are familiar with filter calibers in Europe and the U.S., but to no avail. At one point I considered having S.K. Grimes in Rhode Island make a conversion adapter to 52mm. However, airfares from Japan are too expensive these days, and I have decided not to pursue this plan. I imagine that perhaps this has an unusual thread, but I would appreciate it if someone with more knowledge could enlighten me. I do a lot of outdoor shooting and I don't want to inadvertently damage the lens.

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